std::ranges::copy_n, std::ranges::copy_n_result
| Defined in header <algorithm>
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| Call signature |
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| template< std::input_iterator I, std::weakly_incrementable O > requires std::indirectly_copyable<I, O> |
(1) | (since C++20) |
| Helper type |
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| template< class I, class O > using copy_n_result = ranges::in_out_result<I, O>; |
(2) | (since C++20) |
[0, n). The behavior is undefined if result is within the range [first, first + n) (ranges::copy_backward might be used instead in this case).The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
| first | - | the beginning of the range of elements to copy from |
| n | - | number of the elements to copy |
| result | - | the beginning of the destination range |
[edit] Return value
ranges::copy_n_result{first + n, result + n} or more formally, a value of type ranges::in_out_result that contains an std::input_iterator iterator equals to ranges::next(first, n) and a std::weakly_incrementable iterator equals to ranges::next(result, n).
[edit] Complexity
Exactly n assignments.
[edit] Notes
In practice, implementations of std::ranges::copy_n may avoid multiple assignments and use bulk copy functions such as std::memmove if the value type is TriviallyCopyable and the iterator types satisfy contiguous_iterator. Alternatively, such copy acceleration can be injected during an optimization phase of a compiler.
When copying overlapping ranges, std::ranges::copy_n is appropriate when copying to the left (beginning of the destination range is outside the source range) while std::ranges::copy_backward is appropriate when copying to the right (end of the destination range is outside the source range).
[edit] Possible implementation
struct copy_n_fn { template<std::input_iterator I, std::weakly_incrementable O> requires std::indirectly_copyable<I, O> constexpr ranges::copy_n_result<I, O> operator()(I first, std::iter_difference_t<I> n, O result) const { for (std::iter_difference_t<I> i {}; i != n; ++i, ++first, ++result) *result = *first; return {std::move(first), std::move(result)}; } }; inline constexpr copy_n_fn copy_n {}; |
[edit] Example
#include <algorithm> #include <iomanip> #include <iostream> #include <iterator> #include <string> #include <string_view> int main() { const std::string_view in {"ABCDEFGH"}; std::string out; std::ranges::copy_n(in.begin(), 4, std::back_inserter(out)); std::cout << std::quoted(out) << '\n'; out = "abcdefgh"; const auto res = std::ranges::copy_n(in.begin(), 5, out.begin()); std::cout << "*(res.in): '" << *(res.in) << "', distance: " << std::distance(std::begin(in), res.in) << '\n' << "*(res.out): '" << *(res.out) << "', distance: " << std::distance(std::begin(out), res.out) << '\n'; }
Output:
"ABCD" *(res.in): 'F', distance: 5 *(res.out): 'f', distance: 5
[edit] See also
| (C++20)(C++20) |
copies a range of elements to a new location (niebloid) |
| (C++20) |
copies a range of elements in backwards order (niebloid) |
| (C++20)(C++20) |
copies a range of elements omitting those that satisfy specific criteria (niebloid) |
| (C++20)(C++20) |
copies a range, replacing elements satisfying specific criteria with another value (niebloid) |
| (C++20) |
creates a copy of a range that is reversed (niebloid) |
| (C++20) |
copies and rotate a range of elements (niebloid) |
| (C++20) |
creates a copy of some range of elements that contains no consecutive duplicates (niebloid) |
| (C++20) |
moves a range of elements to a new location (niebloid) |
| (C++20) |
moves a range of elements to a new location in backwards order (niebloid) |
| (C++11) |
copies a number of elements to a new location (function template) |
